One version or another of a magnetic disk storage device has been on the market since about 1956. The size of magnetic storage devices has been successively reduced over time, and recording density has steadily increased. The recording density of magnetic storage devices abruptly accelerated to an annual increase rate of about 60% due to development of a Magneto-Resistive Effect (MR) element in 1992. In addition, the recording density of magnetic storage devices further accelerated to an annual increase rate of about 100% due to the development of a Giant Magneto-Resistive Effect (GMR) element in 1997. However, in the middle of 2000, recording density gradually approached its limit given a conventional magnetic recording principle of longitudinal recording, and increases in the recording density of magnetic storage devices dropped to an increase of about 40% per year. However, since the perpendicular magnetic recording technology was put into practical use in 2005, it is now approximated that growth of the recording density of magnetic storage devices may be recovered to an increase of about 100% per year.
With conventional longitudinal recording technology, magnetic data is horizontally disposed on a disk surface, and magnetic poles of the data bits repel each other which hinder significant increases in recording density. Even if the thickness of a recording medium is reduced to suppress repulsion between magnetic poles of the data bits and higher recording density is achieved, a problem of thermal agitation is not avoidable; that is, recording magnetization may be unstable, even at room temperature. Therefore, it has been difficult to achieve recording densities of more than about 15.5 Gbit/square centimeter (100 Gbit/square inch) with conventional longitudinal recording technology.
On the other hand, unlike longitudinal recording technology, perpendicular recording technology has the following characteristic: as linear recording density is increased, a demagnetizing field exerted between adjacent bits is decreased, and recording magnetization becomes more stabilized. Therefore, perpendicular recording technology has a feature that causes recording magnetization to become more stabile with increases in the recording density, which is effective for achieving ultra-high density recording. In the perpendicular magnetic recording technology, a magnetic field is applied to a recording layer of a two-layer recording medium interposed between a soft-magnetic underlayer and a single-pole head, so that a magnetic material in the recording layer is magnetized in a direction perpendicular to the disk surface and thus information is recorded. Flare point height of a main pole of a perpendicular magnetic recording head is reduced in order to obtain a large recording magnetic field. However, when the height is too low, write blurring may occur in recording, and when the height is too high, the recorded signal may be erased due to residual magnetization.
In longitudinal recording technology, magnetic pole height accuracy, also known as throat height accuracy, is not as stringently defined for the write element. However, in perpendicular recording technology, extremely high accuracy is used for flare point height for the reason set forth above. On the other hand, the read element height uses a high dimensional accuracy in the perpendicular recording technology and in the longitudinal recording technology, which is satisfied simultaneously by accurate definition of the flare point height.
Such dimensions are formed by lapping an air bearing surface of a magnetic head slider to an amount where each element has an appropriate dimension. A method for read element height estimation includes a method where an electric current is directly flowed through an element, and a dimension is calculated from a resistance value of the element. Another method includes flowing an electric current into a guide resistance formed near the element, and a dimension of the guide resistance is calculated from a resistance value thereof, which is assumed to be an estimated value of height of the actual read element. However, a write element is not structured in such a way that electric current flows into the portion to have high dimensional accuracy. In addition, for the write element, a guide resistance is extremely difficult to form in a shape in accordance with a flare point.
As proposed in Jap. Pat. App. No. JP-A-2006-309826, a method of checking a state of a write element without using the guide resistance or the like is given, in which a thin film-like perpendicular magnetic-recording medium (pseudo medium) is formed on an air bearing surface of a magnetic head slider to be examined, and the pseudo medium is subjected to perpendicular magnetic recording from a write element on the magnetic head slider. A write state in the recording is read using a magneto-optical effect microscope or a magnetic force microscope, thereby estimating a magnetic domain structure of the write element. Consequently, quality of a magnetic head is determined. However, in the method, a dimension of an element may not be estimated. In addition, since a medium is used for checking, results of observation and measurements may vary depending on variation in characteristic of an individual medium.
Jap. Pat. App. No. JP-A-2007-122283 discloses a method of measuring distribution of a magnetic field in a plane parallel to an air bearing surface by using a checking medium and a magnetic force microscope (MFM). However, the reference does not describe distribution of a magnetic field in a direction perpendicular to an air bearing surface. Jap. Pat. App. No. JP-A-6-187622 discloses a method, in which an electromagnetic induction magnetic head has one element used as both write and read elements, and the gap depth of a write element is estimated based on characteristics of the relationship between recording current and reading output in the one element. However, the method is unrelated to magnetic field intensity distribution around the write element. Furthermore, Jap. Pat. App. No. JP-A-2000-076633 discloses a method of measuring a recording characteristic of a write element by forming a fixed magnetic sensor within a wafer. However, the method does not allow for estimation of a magnetic field intensity in a three-dimensional space near the write element.
According to S. Y. Yamamoto and S. Schultz, Scanning Magnetoresistance Microscopy (SMRM): Imaging with a MR Head, J. Appl. Phys. 81, 4698 (1997), a method is shown where information recorded in a separately prepared medium is measured and visualized by a different magnetic read/write element. However, even in this case, estimation of an element dimension is not supposed. In addition, since a medium is used for measurement, measurement results may vary depending on the medium.